Remove pan from oven. Cool slightly. Uncover; carefully pour off drippings, leaving pate in pan. Cover pate loosely with foil. Place several heavy cans of food in another 9x5x3-inch loaf pan to serve as weights. Place pan on top of the covered pate. Chill overnight.

Remove weighted pan and foil. Loosen sides if necessary. Invert pate onto a serving platter or wrap in plastic wrap and chill for up to 2 days. Cut pate in half lengthwise and then into thin slices. Serve pate with stone ground mustard.